1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an apparatus and method for driving a liquid crystal display device which is capable of removing motion blurring of an image to improve image quality.
2. Discussion of the Related Art
In general, a liquid crystal display device displays an image by adjusting light transmittance of liquid crystal cells according to a video signal. An active matrix type liquid crystal display device in which a switching element is formed in each liquid crystal cell is suitable for displaying a moving image. As the switching element used in the active matrix type liquid crystal display device, a thin film transistor (hereinafter, referred to as “TFT”) is generally used.
FIG. 1 is a schematic view showing an apparatus for driving a liquid crystal display device of the related art.
Referring to FIG. 1, the apparatus for driving the liquid crystal display device of the related art includes an image display unit 2 including liquid crystal cells which are formed in regions defined by n gate lines GL1 to GLn and m data lines DL1 to DLm, a data driver 4 for supplying an analog video signal to the data lines DL1 to DLm, a gate driver 6 for supplying a scan signal to the gate lines GL1 to GLn, and a timing controller 8 which aligns and supplies externally input data RGB to the data driver 4, generates a data control signal DCS to control the data driver 4, and generates a gate control signal GCS to control the gate driver 6.
The image display unit 2 includes a transistor array substrate and a color filter array substrate facing each other, spacers for uniformly maintaining a cell gap between these two array substrates, and liquid crystal materials filled in the gap provided by the spacers.
The image display unit 2 includes TFTs formed in regions defined by the n gate lines GL1 to GLn and the m data lines DL1 to DLm, and liquid crystal cells connected to the TFTs. The TFTs supply the analog video signal supplied from the data lines DL1 to DLm to the liquid crystal cells in response to the scan signal supplied from the gate lines GL1 to GLn. The liquid crystal cell includes a common electrode and a pixel electrode connected to the TFT with the liquid crystal interposed therebetween and thus may be equivalently expressed by a liquid crystal capacitor Clc. The liquid crystal cell further includes a storage capacitor Cst connected to a previous-stage gate line such that the analog video signal charged in the liquid crystal capacitor Clc is maintained until the next analog video signal is charged.
The timing controller 8 aligns and supplies the externally input data RGB according to the drive of the image display unit 2 to the data driver 4. In addition, the timing controller 8 generates the data control signal DCS and the gate control signal GCS using an externally input dot clock DCLK, a data enable signal DE, horizontal and vertical synchronization signals Hsync and Vsync, and controls the driving timing of the data driver 4 and the gate driver 6.
The gate driver 6 includes a shift register for sequentially generating the scan signal, that is, a gate high signal, in response to a gate start pulse GSP and a gate shift clock GSC in the gate control signal GCS supplied from the timing controller 8. The gate driver 6 sequentially supplies the gate high signal to the gate lines GL of the image display unit 2 and turns on the TFTs connected to the gate lines GL.
The data driver 4 converts the aligned data signal Data supplied from the timing controller 8 into the analog video signal according to the data control signal DCS supplied from the timing controller 8 and supplies the analog video signal of one horizontal line to the data lines DL for each one horizontal period that the scan signal is supplied to the gate lines GL. That is, the data driver 4 selects a gamma voltage having a predetermined level according to the data signal Data and supplies the selected gamma voltage to the data lines DL1 to DLm. At this time, the data driver 4 inverts the polarity of the analog video signal supplied to the data lines DL in response to a polarity control signal POL.
The apparatus for driving the liquid crystal display device of the related art has a slow response speed due to the properties such as inherent viscosity or elasticity of the liquid crystal. That is, the response speed of the liquid crystal varies depending on the physical properties and the cell gap of the liquid crystal material. Conventionally, a rising time is 20 to 80 ms and a falling time is 20 to 30 ms. Since such a response speed of the liquid crystal material is longer than a frame period (NTSC: 16.67 ms) of a moving image, it progresses to the next frame before the voltage charged in the liquid crystal cell reaches a desired voltage, as shown in FIG. 2.
Since the display image of each frame displayed on the image display unit 2 has influence on the display image of the next frame, motion blurring is generated in which the screen is blurred when displaying the moving image on the image display unit 2, due to the perception of a viewer.
Accordingly, in the apparatus and method for driving the liquid crystal display device of the related art, a contrast ratio deteriorates due to the motion blurring generated in the display image and thus image quality deteriorates.
In order to prevent the motion blurring generated in the liquid crystal display device of the related art, a high-speed driving apparatus for modulating a data signal for increasing the response speed of the liquid crystal was suggested.
FIG. 3 is a schematic block diagram showing the high-speed driving apparatus of the related art.
Referring to FIG. 3, the high-speed driving apparatus 50 of the related art includes a frame memory 52 for storing data RGB of an input current frame Fn, a look-up table 54 for comparing the data RGB of the input current frame Fn with data of a previous frame Fn-1 stored in the frame memory 52 and generating modulated data for increasing the response speed of the liquid crystal, and a mixer 56 for mixing the modulated data from the look-up table 54 with the data RGB of the current frame Fn and outputting the mixed data.
In the look-up table 54, the modulated data R′G′B′ having a voltage larger than that of the input data RGB in order to increase the response speed of the liquid crystal to correspond to the gray level of the image, which is rapidly changed, is registered.
Since the high-speed driving apparatus 50 of the related art applies the voltage larger than an actual data voltage to the liquid crystal using the look-up table 54, as shown in FIG. 4, the liquid crystal more rapidly responds to a target gray voltage and, when reaching a desired gray level, the value is maintained.
Accordingly, the high-speed driving apparatus 50 of the related art as shown in FIG. 3 can reduce the motion blurring of the display image by increasing the response speed of the liquid crystal using the modulated data R′G′B′.
However, although the liquid crystal display device of the related art displays the image using the high-speed driving apparatus, the display image is not sharp due to the motion blurring generated in a boundary between the display images. That is, since brightness increases with a gradient in the boundary between the display images, the motion blurring is still generated although the liquid crystal is driven at a high speed.